<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>
<div style="height: 300px;width: 300px;background: red">
  <div style="height: 400px;width: 400px;background: blue">
    <div style="height: 100%;width: 100%;background: black"></div>
  </div>
</div>
</body>
</html>
